Lead alloy amenable to hardening by heat treatment



. in solid solution in lead at the temperature Patented Nov. 4, 1930 UNITED-STATES PATENT err-Ice MIGH AELG. COIRSON, OF. JACKSON HEIGHTS, NEW YORK LEAD ALLOY AMEN-ABLE T0 HARDENING BY HEAT TREATMENT No Drawing.

of heat treatment, remains so initially after quenching and is precipitated in an ultramicroscopic form during aging. These ultramicroscopic particles produce the slip interference effect and harden the alloy. Alloys of this character, as so far described in the literature and patented, sufler from the following drawbacks:

(1) The eutectic point of antimony-lead alloys is located at 243 C. Accordingly, the

' alloys cannot be heat treated at a higher temperature.

(2) The formation of the ultra-microscopic particles of antimony requires only the coming together in no definite proportion of the individual atoms of antimony, and the growth of these particles by the addition of other antimony atoms takes-place whenever any of such atoms and particles come together. Therefore, a further growth of these particles is continuously goingon and both hardness andstrength drop considerably in the course of time. For instance, an alloy that shows a strength of 9800 lbs. per square inch on the tenth day of aging does not show more than 7 500'lbs. after a few weeks" have elapsed.

It has occurred to me that by substituting for the elementary antimony one of its me-' tallic compounds,the second metal of this atoms of the two metals will come together compound also being soluble to a substantial degree ingsolid lead, these two drawbacks might be eliminated due to the following reasons: I (1) The eutectic point would be raised, thereby permitting heat treatment at higher temperatures.

(2) Since the ultra-microscopic particles Application filed June s, 1928. Serial No. 284,004.

which would be precipitated in a lead alloy containing antimony and the second metal would consist of antimony atoms and atoms of the second metal in a definite proportion corresponding to the :atomic proportions of such metals in their metallic compound, such particles would tend to grow only when they should happen to come together with antimony atoms-and atoms of the second metal present in the solid solution of the lead in exactly the proportions such atoms bear towards one another in their metallic compound. As it is extremely improbable that in precisely.theproportions required to produce the definite compound of such metals, the tendency of the ultra-microscopic particles to grow will be substantially prevented.

Starting from this idea I have developed alloys containing lead as a major component and cadmium in addition'to antimony, the I proportion of cadmium to antimony by weight ranging preferably from '1 :1 to 3:2. I found that alloys of this kind have an eutectic point approximately between 280 and 290 C. and, therefore, may be safely heat treated at 270 to 280 C. After this heat treatment has continued for about hour to 1 hour the alloys may be either quenched in water and aged or allowed to cool in air. Both methods lead to the same type of hardening and very high strength figures (8700 lbs. per square inch yield point and 10,800 lbs. per square inch tensile strength) are obtained at the end of the first three hours. These figures. increase further in a slow way only and become 9000lbs. yield point and 11,700 lbs. strength after two days. The storing of these alloys doesnot undermine their properties, i. e., does not weaken them in any degre.

The alloys may contain from 0.5% to 15% cadmium and from 0.5% to-15% antimony. At the lower contents of both additional metals I obtain alloys which are easily rolled into sheet, drawn into wire, extruded ,into tubes, etc. With the higher amounts of both metals I obtain alloys which have a strucbearing metal. aware of the fact that the presently used lead base bearing alloys containing antimony or antimony plus tin develop primary crystals of either antimony or a tin-antimony compound, which latter act as thehard constituent in the soft matrix. These constituents are however, specifically much lighter than lead and tend to'segregate. In my alloys the hard constituent or the cadmium-antimony compound is also much lighter than lead but shows however a tendency to crystallize in such a manner as to form cellular aggregates, with the surrounding lead eutectic. Therefore, they remain very evenly distributed through the whole alloy.

When an alloy capable of being rolled or otherwise worked is desired, it is preferred to maintain the proportion of antimony between 0.5-and 5% and that of cadmium between .0.5 and 5%. An alloy combining the highest strength with a suflicient elongation of any thus produced by me contained about 1% cadmium and about 1% ant-imony. I have found that the ductility of the alloy decreases with the increase of antimony above 1%. On. the other hand, increase of the amount of cadmium does not have much influence on ductility unless such increase is accompanied by decrease of the amount of antimony to less than 1%, in which event the strength drops and the elongation increases. r

A number of tests of lead alloys containing antimony and cadmium within the range specified, and rolled into sheet form, heat treated and aged according to the method above outlined, has shown the following average properties for the product;

Tensile strength 11,000 lbs/sq. in. Yield point 8,900 lbs/sq." in. Elongation in 2; 12.5% Area reduction 2 5.0% Brinell (1/16" ball).

(2 kgs. load) 27.0

When the alloy contains from.5 to each of cadmium and antimony a material suitable as a bearing metal in the cast state tures down to 200 C.

In this connection, I am be produced by'heating at lower tempera- It is understood that various modifications I in the proportions of the various metals in the alloys may be made, and that various details of the method of heat treating may be modified without departing from the scope of the invention which is not to be deemed as limited other than as indicated in the appended claims.

What I claim is: 7

1. A method of hardening an alloy consistingprincipally of lead, and containing 0.5 to 15% each of antimony and cadmium, which comprises heating said alloy to a temperature upwards of 200 C. and short of the melting point for a sufficient period of time to bring the antimony and cadmium into solid solution in the lead matrix and then cooling to produce supersaturation followed by aging.

2. A method of hardeningan alloy consisting principally of lead, and containing 0.5 to 15% each of antimony andv cadmium, which comprises heating said alloy at from 270 to 280 C. for at least minutes, and thereafter quenching to produce supersaturation followed by aging.

3. A hardened and worked metal article consisting principally of lead and containing approximately 1% eachofantimony and cadmium, and-characterized by a physical structure and properties such as are produced 'when an alloy of like composition is subjected to heat treatment at such a temperature and for such time as to bring the antimony and cadmium'into; solid solution in the lead, followed by cooling to produce supersaturation and then by a'ging.

4. A hardened and Worked metal article consisting principally of lead-and containing 0.5% to 5% each of antimony and cadmium, and characterized by a physical structure and properties such as are produced .when an alloy of like composition 1s sub-v jected to heat treatment atsuch a temperature and for such time as to bring the antimony and cadmium into solid solution in the lead, followed by cooling to produce supersaturation and then by aging.

In testimony whereof, Ihave signed my name to this specification this 4th day of June, 1928.

MICHAEL G. CORSON. 

